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Surface functionalization of nanomaterials and the development of nanobiosensors

SURFACE FUNCTIONALIZATION OF NANOMATERIALS
AND THE DEVELOPMENT OF NANOBIOSENSORS
by
RUI ZHANG
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
December 2012
Copyright 2012 RUI ZHANG

In the past 20 years, material scientists and engineers have progressively miniaturized the materials that constitute the building blocks of various biomedical devices. This progressive downscaling has led to the creation of materials with at least one critical dimension falling within the 1-100 nm range. These nanomaterials have been considered as ideal candidates for biosensing applications due to their high surface-to-volume ratio and small sizes. A diversity of sensor architectures has been designed and fabricated during the last decade that utilizes different nanomaterials as sensing elements. Among them, sensors based on FETs have drawn increasing attention because of their capability of performing rapid and label-free detections. Since the first demonstration of FET-based biosensors in 2001, people have achieved detections of proteins, oligonucleotides and viruses with high sensitivity and selectivity. However, to facilitate the widespread adoption of nanobiosensing technology, researchers still need to address a few challenges, including multiplexing, cost efficiency and signal reproducibility. This dissertation tries to tackle these challenges by improving nanosensor fabrication techniques and developing novel surface functionalization methods. ❧ Chapter 1 briefly introduces the fundamentals of nanobiosensors, including nanomaterial synthesis, device fabrication and sensing setup, and discusses current challenges in the nanobiosensing field. ❧ Chapter 2 describes a newly designed electroactive surface modifier that can be used in selective biofunctionalization of nanomaterials. This molecule offers promising control over the surface reaction of each sensor in an array and can be considered as a key element in the fabrication of high-density biosensor arrays for multiplexed biosensing in the future. ❧ Chapter 3 focuses on sensing platforms based on solution grown ZnO nanostructures. Mass production of ZnO nanowires and nanobelts are prepared using a low cost, low temperature hydrothermal method, and used to fabricate back-gated FETs. By applying a post-synthesis annealing step to the ZnO products, we adjust the doping level of the nanowires and nanobelts, and thus significantly improve their electrical properties. These FETs shows comparable performance with those based on ZnO nanostructures synthesized via vapor-phase approaches. ❧ Chapter 4 introduces a new class of small affinity binding agents, cyclotides, as capturing probes in nanobiosensing. These backbone-cyclized polypeptides with a disulfide-stabilized core are chemically more stable than conventional antibodies and can be produced in relatively large quantities at low cost. A cyclotide, MCoTI-II, was integrated with In₂O₃ NW mats and sensors for trypsin sensing in this chapter. ❧ In the end, chapter 5 studies top-down polysilicon nanoribbon sensors and their sensing applications. Top-down sensors are believed to have better device uniformity and thus can yield more reliable sensing signals. In this chapter, polysilicon nanoribbon FETs are fabricated using a simple two-mask photolithography method on a wafer scale and functionalized with and without the native oxide coating. The pH sensing and biosensing performed with these sensors demonstrates their promising sensitivity and selectivity.

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SURFACE FUNCTIONALIZATION OF NANOMATERIALS
AND THE DEVELOPMENT OF NANOBIOSENSORS
by
RUI ZHANG
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
December 2012
Copyright 2012 RUI ZHANG